Force MimeHandlerView to always use BrowserPlugin

content/browser/frame_host/render_widget_host_view_child_frame.cc

Index: content/browser/frame_host/render_widget_host_view_child_frame.cc
diff --git a/content/browser/frame_host/render_widget_host_view_child_frame.cc b/content/browser/frame_host/render_widget_host_view_child_frame.cc
index 15fbdb9edea36181badc0efd6498b90daface0e8..e32588225a3f532e2c437e9ef0cf349451e0a97b 100644
--- a/content/browser/frame_host/render_widget_host_view_child_frame.cc
+++ b/content/browser/frame_host/render_widget_host_view_child_frame.cc
@@ -209,7 +209,12 @@ gfx::Vector2dF RenderWidgetHostViewChildFrame::GetLastScrollOffset() const {
 }
 
 gfx::NativeView RenderWidgetHostViewChildFrame::GetNativeView() const {
-  NOTREACHED();
+  // TODO(ekarmaad): To accomodate MimeHandlerViewGuest while embedded inside
+  // OOPIF-webview, we need to return the native view to be used by
+  // RenderWidgetHostViewGuest. Remove this once https://crbug.com/563285 is
+  // fixed.
+  if (frame_connector_)
+    return frame_connector_->GetParentRenderWidgetHostView()->GetNativeView();
   return nullptr;
 }